1. Field of the Invention
The present invention relates to a film formation apparatus for a semiconductor process for forming a thin film of a high-dielectric-constant material on a target substrate, such as a semiconductor wafer, and also to a method of using the apparatus. The term “semiconductor process” used herein includes various kinds of processes which are performed to manufacture a semiconductor device or a structure having wiring layers, electrodes, and the like to be connected to a semiconductor device, on a target substrate, such as a semiconductor wafer or a glass substrate used for an LCD (Liquid Crystal Display) or FPD (Flat Panel Display), by forming semiconductor layers, insulating layers, and conductive layers in predetermined patterns on the target substrate.
2. Description of the Related Art
In manufacturing semiconductor devices, processes, such as CVD (Chemical Vapor Deposition), are performed to form thin films of various kinds on a target substrate, such as a semiconductor wafer. For example, a film formation process of this kind is arranged to form a thin film on a semiconductor wafer, as follows.
At first, the interior of the reaction tube (reaction chamber) of a heat-processing apparatus is heated by a heater at a predetermined load temperature, and a wafer boat that holds a plurality of semiconductor wafers is loaded. Then, the interior of the reaction tube is heated up to a predetermined process temperature, and gas inside the reaction tube is exhausted through an exhaust port, so that the pressure inside the reaction tube is reduced to a predetermined pressure.
Then, while the interior of the reaction tube is kept at the predetermined temperature and pressure (kept exhausted), a film formation gas is supplied through a process gas feed line into the reaction tube. For example, in the case of CVD, when a film formation gas is supplied into a reaction tube, the film formation gas causes a thermal reaction and thereby produces reaction products. The reaction products are deposited on the surface of each semiconductor wafer, and form a thin film on the surface of the semiconductor wafer.
Reaction products generated during the film formation process are deposited (adhered) not only on the surface of the semiconductor wafers, but also on, e.g., the inner surface of the reaction tube and other components in the tube, the latter being as by-product films. If the film formation process is continued while by-product films are present on the interior of the reaction tube, the by-product films partly separate therefrom and generate particles. The particles may drop onto the semiconductor wafers, and reduce the yield of semiconductor devices being fabricated.
In order to solve this problem, cleaning of the interior of the reaction tube is performed after the film formation process is repeated several times. In this cleaning, the interior of the reaction tube is heated at a predetermined temperature by a heater, and a cleaning gas is supplied into the reaction tube. The by-product films deposited on the inner surface of the reaction tube are dry-etched and removed by the cleaning gas. Jpn. Pat. Appln. KOKAI Publication No. 3-293726 (Patent document 1) discloses a cleaning method for removing by-product films, which contain silicon nitride as the main component, by a mixture gas of fluorine gas and a halogen-containing acid gas. However, as described later, the present inventors have found that this method cannot practically remove certain types of by-product films, such as those containing as the main component (i.e., at 50% or more) a high-dielectric-constant material (having a dielectric constant of 7 or more, hereinafter), which attracts attention in recent years.